1. Field of the Invention
The present invention relates to a liquid discharge head substrate for discharging a liquid, a liquid discharge head using the substrate, and a manufacturing method therefor.
2. Description of the Related Art
As a liquid discharge head for discharging a small amount of liquid, an ink jet head for discharging ink using heat energy is known. In recent years, there has been a demand for increasing speed of recording by an ink jet recording apparatus using the ink jet head. For this reason, a drive frequency for driving a heating resistor layer of the ink jet head has been increased, or the number of discharge ports has been increased. However, in order to provide a large number of discharge ports to a head substrate having a certain size, it is necessary to make a width of a wiring narrower, which results in increasing a wiring resistance. As a simple method of preventing the wiring resistance from increasing due to the narrowed wiring width, a height of the wiring is increased (thickness of wiring layer is increased).
Herein, a laminated structure in the vicinity of a heating portion is described with reference to FIG. 13 which is a schematic cross-sectional diagram of a conventionally known ink jet head for discharging ink using heat energy.
On an Si substrate 120, a heat accumulation layer 106 formed of an SiO2 film which is formed by thermal oxidation or the like is formed. On the heat accumulation layer 106, a heating resistor layer 107 for applying heat energy to ink, and wirings 103 and 104 for applying a voltage to the heating resistor layer 107 are formed. A portion of the heating resistor layer 107 which is exposed from the wirings 103 and 104 becomes a heating portion 102. In addition, on the heating resistor layer 107 and the wirings 103 and 104, an insulating protective film 108 for protecting the heating resistor layer 107 and the wirings 103 and 104 is provided. Further, on the insulating protective film 108, a Ta film 110 serving as a cavitation resistant film is provided.
On the heating portion 102, an ink flow path (not shown) is formed. The heating portion 102 is in contact with the ink, with the result that the heating portion 102 may be chemically damaged due to corrosion or the like which is caused when the wirings 103 and 104 and the heating portion 102 that are made of metal are brought into contact with the ink, or may be physically damaged by foaming of ink. The insulating protective layer 108 for protecting the heating portion 102 and the wirings 103 and 104 from the damages and the Ta film 110 serving as an upper portion protective film 110 are formed. A portion of the Ta film 110, which is in contact with the ink and is provided on the heating portion 102, corresponds to a heat acting portion.
In the ink jet head substrate having the above-mentioned structure, in a case of forming a protective layer (protective film) for protecting the wirings stacked on the substrate from a liquid such as ink (preventing the wirings from being in contact with ink or the like), when a step of the wirings, that is, a height of the wirings, becomes smaller, more excellent step coverage of the protective layer is obtained.
Among the conventional methods of forming a protective layer (insulating protective layer), as a method capable of forming the protective layer by lowering the temperature (450° C. or lower), an atmospheric pressure CVD method, a plasma CVD method, and a sputtering method are known. However, the atmospheric pressure CVD method has a problem in that taper coverage is deteriorated while the substrate is less damaged. The plasma CVD method and the sputtering method each have a problem in that high energy is applied to particles and the particles are stacked on the substrate, which damages a substrate surface. An example of a method in which a damage to a substrate is relatively small includes a low pressure CVD method. However, the low pressure CVD method requires higher temperature of about 800° C., so it is difficult to deposit an insulating film after formation of the wirings made of metal materials.
Further, it is said that, in a case of forming a film, e.g., silicon oxide film by each of the methods, denseness thereof becomes smaller in the following order of the thermal oxidation method, the low pressure CVD method, the atmospheric pressure CVD method, and the plasma CVD method.
Conventionally, the protective layer of the above-mentioned ink jet head is formed by the plasma CVD method, but a layer quality (film quality) of the protective layer thus formed can be enhanced by setting film formation temperature higher. Specifically, when an alloy of aluminum, silicon, or the like, or silicide such as titanium silicide having heat resistance is used for wirings, the film formation temperature can be set higher.
However, the alloy of aluminum, silicon, or the like, or silicide such as titanium silicide has higher resistance than aluminum, which makes the height of the wirings higher and requires higher coverage of the protective layer. When aluminum or an aluminum alloy is exposed to the higher temperature, convex portions having sharp-pointed edges called “hillock” are formed to thereby lose evenness of the surface. In order to suppress formation of the hillock, it is necessary to further increase the layer thickness (film thickness) of the protective layer to be formed on the wirings made of aluminum or an aluminum alloy, contrary to the demand for making a layer thinner (making film thinner). In view of the above, it is difficult to enhance the film quality of the protective layer while increasing the film formation temperature.
Further, the protective layer formed by the plasma CVD method does not have a film quality with a required denseness, which raises the following problems.
1. While the protective layer has a certain protective function with respect to ink, the film may be eluted with respect to an ink of some kind.
2. A step portion does not constantly have sufficient coverage, so ink enters from a portion having insufficient coverage, which may lead to breaking of wirings.
3. The protective layer is scraped off during a process of repeating foaming and defoaming of ink due to insufficient cavitation resistance. Accordingly, the protective layer made of metal such as Ta having higher cavitation resistance is required.